Want to reduce the build size of your Unity mobile app by up to 70%?

By Ghost / 27 Jan 2020

Topics: augmented reality | blog | design | experience | hardware

As a developer, I have worked on multiple projects and platforms such as  Hololens , Oculus Quest & Go , iOS , Android etc. And all platforms have their own pros, cons and restrictions.

“Size doesn’t matter” is a popular saying, but when you work on a mobile platform like iOS or Android, size does matter. The size of your app will determine whether it gets downloaded or not. The smaller the build size of your app, the greater the chance for it to be  downloaded.

Today, I would like to share an effective way to reduce the build size of your mobile applications.

As a developer, we spend a lot of time developing an application or game. And more and more features are often added into the app or game to make it better than competing apps on the market.

If it’s a game, more characters and animations may be added. Or for apps, perhaps connectivity with social networking platforms like Whatsapp, Facebook or Instagram is desired.

Whether working on an application or a game, all developers really want is an attractive UI and graphics with multiple screens and smooth transition animations.

Multiple UI elements are often added into a  game/app to make it look more attractive. But,  all developers know that if you add more and more UI elements,  it starts to make the app slow and sluggish,it requires increasingly powerful hardware to run smoothly and increases the build size of the app/game.

For a developer that's a bad outcome  because we want to target the maximum  number of devices possible and want the build size to be as low as possible so the maximum number of people will install it .

There is a simple method  that can help you reduce the build size and frame rate of your app. It's called a "sprite atlas."

What is Sprite Atlas and  how it works ?

This is a 4k sprite atlas containing 28 images at 540x960

When you start working on your app, you can access  all the screens your app will have  and the related UI assets (sprites) from the graphics designer.

For example, your app may have  10 different screens and each screen may have 4-5 different UI elements (like a button or loading bar etc.) resulting in  40 to 50 different  sprite assets. Each sprite asset has its own size and it gets added to your app's overall build size .

And generally in Unity, one image is equal to one batch. If the screen has 10 different UI elements, there will be at least 10 batches only for the UI .  What you can do is ask your graphics designer (or do it yourself) to  make a bigger POT image for each screen which will contain all the images related to that screen.

This big POT image is called a sprite atlas. Sprite atlases are very useful because they  reduce  the number  of batches and because of the POT image, the overall build size also gets reduced.

I would like to share one of my experiences. During one of my projects requiring multiple animations such as coin splashes and confetti etc., I used Unity sprite animations. Each animation was a minimum of 2 seconds  with 30 FPS.

Because of this, I was left with  hundreds of sprite assets in my project, and the install size of my app reached over 500 MB (before sprite animation size was 250 mb ), which was very undesirable. I then  used the sprite atlas technique to reduce the size of the build, and it also helped me to reduce the batches too.

From my experience,  I would suggest making sprite animations at 28 fps and a size of 540x960  for individual sprites. This is best for animations  because it maintains  good quality on bigger screens too (no  blurring due to scaling ). I use  TexturePacker for making the sprite atlases. It's a really cool tool and it’s free as well. Here is a helpful l post from where I learned the different possible ways to make sprite atlases for U .

Before and after using Sprite atlas

Conclusion

  • Always use sprite atlases for the UI for the app -- ideally one sprite atlas for each screen.
  • For 2D sprite animations in Unity, also use sprite atlases, make the animation 28 FPS. The ideal size of individual sprites is 540x960 because it isn't too  small or large so scaling due to different screen sizes will not matter much.
  • A 4K sprite atlas  will be of 8MB in Unity , 2K of 2MB and 1K of 0.5MB.
  • Don't use 8K sprite atlases in Unity as I have tried it and it gives a weird bug.

Try sprite atlases in your Unity project and please comment and share if  this post helps you.

Ghost

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